(1) Field of the Invention
The present invention relates to a novel hardening material. More particularly, the present invention relates to a hardening material having excellent performances as a bone-restoring hardening material. More specifically, the present invention provides a hardening material comprising (a) a powder component composed of a powdery mixture of tetracalcium phosphate and calcium phosphate having a Ca/P atomic ratio lower than 1.67 and (b) a liquid component composed of a colloidal aqueous solution comprising solid colloid particles dispersed in an aqueous medium, wherein said components (a) and (b) are independently packed and both the components are mixed for hardening.
(2) Description of the Related Art
Various hardening materials have been developed and practically used. However, few of them are satisfactorily used in the fields where a high strength is required, for example, for restoring hard tissues of a living body, e.g., setting a broken bone or filling a tooth defect. At the present, development of a hardening material capable of exhibiting a high strength is especially desired in the field of therapeutic materials, for example, medical materials such as a filling material for a bone defect and a luting filling material for an artificial bone or artificial articulation, and dental materials such as a luting cement, a filling cement, a temporary sealing cement, a root canal filling material and a cavity lining material. Materials used in this field are required to have a good affinity with a tooth or bone and a much reduced harmful effect and show a high strength.
As the hardening material to be used in this field, there have been proposed materials forming hydroxyapatite which is a main component of teeth or bone. For example, a hardening material comprising tetra calcium phosphate, calcium hydrogenphosphate anhydride or dihydrate and water forms hydroxyapatite and hardens when mixed (see U.S. Pat. No. 4,518,430 and U.S. Pat. No. 4,612,053).
In the hardened body obtained from this hardening material, in general, the strength is not sufficiently improved, and this hardening material is defective in that the hardening material cannot be applied to a part for which a high strength is required. As the material for improving the strength, there has been proposed a hardening material comprising powdery tetracalcium phosphate as the powder component and an aqueous solution of an organic acid such as citric acid, succinic acid or malic acid as the liquid component (see Japaneses Unexamined Patent Publication No. 62-72363). However, this hardening material is defective in that since a calcium salt of the organic acid is formed as a by-product and the obtained hardened body comes to have a high water solubility, when the material is used as a dental filling material, the hardened body is dissolved during a long period of time.
Furthermore, use of an aqueous solution of a polymer of an unsaturated carboxylic acid as the liquid component has been proposed (Japanese Unexamined Patent Publication No. 62-72363). However, according to this proposal, a harmful effect of causing inflamation in a living body tissue by the unreacted carboxylic acid is brought about at the initial stage of mixing, and the proposed hardening material is not completely satisfactory.